American military officials say Israel launched a major military exercise that appeared to be aimed in part at demonstrating its ability to stage an attack on Iran's nuclear facilities.

Israel's military refused to publicly confirm or deny whether the exercise was a rehearsal for a potential bombing attack.

But a senior Israeli Air Force official close to the operation told FOX News that the military is preparing for all possibilities with Iran, and during this exercise was testing its refueling capabilities. The source said helicopters were even used to practice how to respond to a downed plane.

An Israeli fighter pilot also confirmed to FOX News that he took part in the mock air mission in mid-May. Pentagon officials said Israel sent dozens of aircraft on the large-scale mission in the eastern Mediterranean.

The aircraft used in the drill, F-15s and F-16s, flew a distance of about 900 miles — similar to the distance between Israel and uranium-enrichment facilities at Natanz, Iran, officials said.

One defense official said the exercise could be taken as a show of force to Iran and a demonstration to the world that Israel is serious about the need to challenge the country's nuclear program — and might be prepared to do so militarily.

"They have been conducting some large-scale exercises — they live in a tough neighborhood," one U.S. official said, though he offered no other recent examples.

Another defense official told FOX News that the "dry run" was the second time in three months Israel has carried out such a drill. The official said the reports on the mission were probably the result of a deliberate leak from the Pentagon to send a signal to Iran — and even Israel — about a potential strike against Iran.

Privately, Pentagon officials grimace at the idea of Israel striking Iran, fearing the unintended consequences of such an attack.

The Jerusalem Post reported that a senior cleric in Iran warned Israel, in response to the drill, that it would react to such a strike with a "strong blow."

The New York Times first reported Friday that more than 100 Israeli fighter jets took part in the maneuvers over the eastern Mediterranean and Greece. Citing undisclosed American officials, it said the exercise appeared to be an effort to focus on long-range strikes.

"They wanted us to know, they wanted the Europeans to know and they wanted the Iranians to know," a Pentagon official told the Times. "There's a lot of signaling going on at different levels."

The newspaper reported the drill was executed in June, but the senior Israeli source told FOX News it was actually carried out in May.

The source said the air force got permission from the countries along the Mediterranean to fly the mission. The Israeli Air Force needed permission to conduct the exercise from all the countries whose air space was entered, according to the official. The Israeli planes flew above civilian air space to avoid disrupting any passenger jets.

Click here to read the full story in The New York Times.

U.S. officials, however, did not believe Israel had decided to attack Iran or think such a strike was imminent.

Asked to comment, the Israeli military issued a statement saying only that the Israeli air force "regularly trains for various missions in order to confront and meet the challenges posed by the threats facing Israel."

Israeli military analyst Martin Van Creveld of Jerusalem's Hebrew University said military preparations for a possible attack are indeed under way.

"Israel has been talking about this possibility for a long time, that it would not take an Iranian nuclear weapon lying down. And it has been practicing the operation or operations for a long time," he said.

But though an Israeli strike would likely be able to "paralyze the most important Iranian nuclear installations," it probably won't be able to destroy the program entirely, Van Creveld said.

"I would be very surprised if Israel can really knock out every part of this program, which by all accounts appears to be large and well-concealed and well-dispersed," he said.

Israeli government spokesman Mark Regev offered no comment beyond the military's statement.

Israeli Prime Minister Ehud Olmert has said he prefers that Iran's nuclear ambitions be halted by diplomatic means, but has pointedly declined to rule out military action.

In an interview with the German magazine Der Spiegel published on Wednesday, Olmert said the current international sanctions against Iran would probably not succeed alone, adding there were "many things that can be done economically, politically, diplomatically and militarily."

Asked if Israel was capable of taking military action against Iran, Olmert said, "Israel always has to be in a position to defend itself against any adversary and against any threat of any kind."

Russia's foreign minister is warning against the use of force on Iran, saying there is no proof it is trying to build nuclear weapons with the program Tehran said is for generating power.

There are precedents for unilateral Israeli action in such cases. In 1981, Israeli jets bombed Iraq's Osirak nuclear facility to end dictator Saddam Hussein's nuclear program. And last September Israel bombed a facility in Syria that U.S. officials said was a nuclear reactor being constructed with North Korean assistance.

A U.S. intelligence report released late last year concluded that Iran has suspended its nuclear weapons program, but Israeli intelligence believes that assessment is incorrect and that work is continuing.

FOX News' Jennifer Griffin and The Associated Press contributed to this report.